Strange AI frequency behaviour

I have AI aircraft that change over to the frequency 199.990 and when this happens they then maintain the altitude they were at, eg A070 when they should be climbing up into the flight levels.As well as this, they drop speed to well below what they should be doing, AND maintain there current heading sometimes flying upwards of 40nm off track.They then get the instruction to resume own navigation. Then the frequency jumps back to the frequency they should be on and they resume normal flight, re. nav, speed and altitude. (i have a utility similar to TCAS that displays other AI aircraft, giving their airspeed, altitude, callsign and frequency)RC4 doesnt assign them that frequency, in other words i never hear them get handed off. I just notice them flying in this erratic manner and notice that strange frequency.Its the frequency that leads me to believe that something is out of the ordinary. Is there something simple that im not seeing?Thanks in advance for help.Pan Pan Pan